This invention relates generally to an apparatus and system for producing a more accurate calibration gas that is used to calibrate analytical instruments. A method of producing such calibration gas is also contemplated. This invention enables enhanced quality control and product end quality. The apparatus and system are particularly well suited for devices that emit gas(s) at a constant rate, and particularly, to commercially available gas emitting devices that are used to produce calibration gases for various types of gas or liquid analyzers. The gases are typically emitted from such a device through a permeable material, and mixed with a moving fluid medium, such as gas to form a calibration standard for use in an analyzer or other instrument.
As such, control of the temperature environment where such devices are used is extremely important to get a more reliable and steady diffusion of such standards, and further as such standards are relatively expensive, the reliable life of the standards can be prolonged by keeping the standards in a temperature controlled environment.
In prior art practices, it was not uncommon to leave the permeation devices in ambient air temperatures when the devices were not being used. Further, it was not uncommon to use tubing that connected a gas source to the permeation device and then to the instrument, mid-air and subjected to varying ambient air temperatures. Further, if an air conditioner or heater turned on, or the ambient room temperature was otherwise changed, the permeation device would be subjected to varying temperatures. The temperature would often be measured at the point of the tube hanging in mid-air, which would not be entirely accurate because sudden temperature changes could change the characteristics of the permeation device. Further, gas flow might be estimated, or a flow meter might be used.
Also, the permeation devices might have been subjected to different temperatures overnight (cooler or hotter temperatures, e.g., due to seasonal temperatures), even though climate control systems may have warmed or cooled the environment a few hours or less before use. Thus, the permeation device might take hours, or even half a day to actually reach equilibrium and a steady diffusion rate. Thus, by keeping the permeation device at a constant, controlled temperature, the devices are not subjected to temperature extremes that can cause miscalibrations.
Importantly, another critical parameter for proper operation of the permeation standard is the flow rate. Applicants' apparatus, method, and system include a means for controlling the flow rate of the fluid medium as well as the temperature of the permeation device and the gas that mix with the impurity source.
Preferably, a semi-conductor cooling and heating device is used in conjunction with Applicants' invention. The semi-conductor device is small, efficient, and economical to use.
While certain prior art apparatus exist, they are limited in their function. For example, the prior art apparatus and methods only include heating means, while Applicants' invention also focuses upon cooler temperatures ranges. This is especially advantageous for certain types of permeation devices and in situations where the ambient temperature exceeds the optimal temperature range for operation of the permeation devices.
Furthermore, because the apparatus and system is preferably kept in an operative standby mode when calibration is not needed, the apparatus can be easily and quickly shifted to a calibration mode by changing the source of gas that flows through the apparatus and system.